Spontaneous preterm birth (SPTB) affects more that 12 percent of all births among urban women and contributes to more than one-third of all infant deaths. Numerous adverse pregnancy outcomes have been prospectively linked to BV including SPTB. Despite the consistently strong epidemiologic link between BV and SPTB, many BV positive pregnant women deliver healthy, term infants and the current treatment options for BV are largely ineffective. Microbiologic variations exist among BV positive women and this variability may explain the limited effectiveness of metronidazole in curing BV and/or reducing SPTB risk. The aims of this amended, competing continuation application are: 1) to evaluate whether Gardnerella vaginalis, Mobiluncus curtisii, Atopobium vaginae, Leptotrichia amnionii, and the Clostridiales bacteria designated Bacterial Vaginosis-Associated Bacterium (BVAB) 1,2 or 3 measured in the first trimester of pregnancy are important, independent predictors of SPTB, and 2) to evaluate whether consistently high levels of Gardnerella vaginalis, Mobiluncus curtisii, Atopobium vaginae, Leptotrichia amnionii, and Bacterial Vaginosis-Associated Bacteria (BVAB) 1,2 or 3, measured at two points during pregnancy, are an important, independent predictor of SPTB. Women attending their first prenatal care visit at Temple University with a pregnancy of 12 weeks gestation or less will be recruited. Baseline data collection will be standardized and include a structured in- person interview, buccal swab for genotyping of three inflammatory genes, and vaginal swabs to detect the presence and degree of BV based on Gram stain. In addition, the concentrations of selected vaginal bacteria will be measured using PCR assays targeting 16S rRNA genes from the BV-associated bacteria of interest. Repeat vaginal swabs will be collected between18-20 weeks gestation to examine the change in these bacteria and the role of consistently high levels of BV-associated bacteria and SPTB risk. In this case-cohort study, we will enroll and classify 2200 pregnant women over a three year period and randomly sample 20 percent of the underlying population to generate the subcohort. We will identify all SPTB cases occurring within and outside the subcohort and compare the results to the remaining subcohort. Given the public health impact of high rates of infant morbidity and mortality due to SPTB, these results may identify a group of women at high risk of SPTB based on early pregnancy BV profile characteristics. These results will also examine the biologic mechanisms and co-factors most responsible for the increased risk of SPTB among urban, BV positive women and the ineffectiveness of current BV treatment options. PUBLIC HEALTH RELEVANCE: Spontaneous preterm birth (SPTB) affects more that 12 percent of all births and contributes to more than one-third of all infant deaths. Despite the consistently strong epidemiologic link between BV and SPTB, many BV positive pregnant women deliver healthy, term infants. The results from this study will add valuable information regarding the specific BV-associated bacteria most related to SPTB and may explain the current limited effectiveness of BV treatment in reducing the risk of SPTB.